Touch detection circuit with different charging and discharging currents and operating method thereof

ABSTRACT

There is provided a touch detection circuit including a charging circuit, a discharging circuit, a counter and a processor. The charging circuit charges a detection capacitor within a charging interval using different currents. The discharging circuit discharges the detection capacitor within a discharging interval using different currents. The counter counts the charging interval and the discharging interval. The processor subtracts a baseline time from a counted charging time and a counted discharging time to cancel the noise interference.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/930,348 filed on Jul. 16, 2020, the disclosureof which is hereby incorporated by reference herein in its entirety.

BACKGROUND 1. Field of the Disclosure

This disclosure generally relates to a touch detection circuit and, moreparticularly, to a touch detection circuit with a detection capacitorbeing charged and discharged using different currents.

2. Description of the Related Art

The capacitive touch circuit detects a touch according to thecapacitance variation caused by a conductor approaching thereto.Therefore, a capacitive touch circuit can be used as a capacitiveswitch, e.g., arranged on a door handle for detecting whether there istouch by a human body.

In the cases that the capacitive switch is used in outdoor environment,because the capacitance variation of the capacitive switch can have asignificant change due to the significant fluctuation of environmentalparameters including temperature and humidity, the detection correctnessis degraded.

Furthermore, when the capacitive switch is used in the environment withhigh noises, a time interval counting the capacitance variation ispossibly affected by noises to cause identification error. For examplereferring to FIG. 1 , it is a schematic diagram of charging anddischarging of a conventional capacitive switch. A charging interval Tris defined as a time interval that a capacitor voltage reaches areference voltage V_(H). It is seen from FIG. 1 that when the capacitiveswitch receives external noises, the time interval that the capacitorvoltage reaches V_(H) is shortened, and thus the identification error isoccurred.

Accordingly, it is necessary to provide a touch detection circuitcapable of eliminating the environmental change and noise interference.

SUMMARY

The present disclosure provides a touch detection circuit that chargesand discharges a detection capacitor using two different currents, andcancels the baseline count during the touch identification to improvethe detection accuracy.

The present disclosure further provides a touch detection circuit thatavoids the noise frequency by changing charging and discharging currentsthereby improving the detection accuracy.

The present disclosure provides a touch detection circuit including adetection chip. The detection chip is configured to be coupled to anelectrode; charge the electrode within a first charging interval using afirst charging current, and charge the electrode using a second chargingcurrent, smaller than the first charging current, till a first referencevoltage is reached; discharge the electrode within a first discharginginterval using a first discharging current, and discharge the electrodeusing a second discharging current, smaller than the first dischargingcurrent, till a second reference voltage, which is smaller than thefirst reference voltage, is reached; and identify approaching of theexternal conductor according to a second charging interval during whichthe electrode is charged by the second charging current and a seconddischarging interval during which the electrode is discharged by thesecond discharging current without according to the first charginginterval and the first discharging interval.

The present disclosure further provides a capacitive switch including anelectrode and a detection chip. The electrode has capacitance. Thedetection chip is coupled to the electrode, and configured to charge theelectrode sequentially using a first charging current and a secondcharging current, smaller than the first charging current, within acharging interval, discharge the electrode sequentially using a firstdischarging current and a second discharging current, smaller than thefirst discharging current, within a discharging interval, exclude timeintervals associated with the first charging current and the firstdischarging current from a summation of the charging interval and thedischarging interval to determine a time of interest, and output acontrol signal by comparing the time of interest with a variationthreshold.

The present disclosure further provides an operating method of a touchdetection circuit. The touch detection circuit includes an electrode anda detection chip. The operating method includes the steps of: charging,using the detection chip, the electrode using a first charging currentwithin a first charging interval; charging, using the detection chip,the electrode using a second charging current, smaller than the firstcharging current within a second charging interval; discharging, usingthe detection chip, the electrode using a first discharging currentwithin a first discharging interval; discharging, using the detectionchip, the electrode using a second discharging current, smaller than thefirst discharging current, within a second discharging interval; andidentifying a touch event according to a time variation of multiplesummations of the second charging interval and the second discharginginterval.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of charging and discharging of aconventional capacitive switch.

FIG. 2 is a schematic block diagram of a touch detection circuitaccording to one embodiment of the present disclosure.

FIG. 3 is a schematic diagram of a current source circuit of a touchdetection circuit according to one embodiment of the present disclosure.

FIG. 4 is a schematic diagram of charging and discharging of a touchdetection circuit according to one embodiment of the present disclosure.

FIG. 5 is a flow chart of an operating method of a touch detectioncircuit according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

The touch detection circuit of the present disclosure is applied to, forexample, a capacitive switch capable of cancelling the noiseinterference. The touch detection circuit is especially suitable to anapplication operated under large fluctuation of environmental parameterand high external noises. By cancelling the baseline voltage, thedetection accuracy is improved.

Referring to FIG. 2 , it is a schematic block diagram of a touchdetection circuit 200 according to one embodiment of the presentdisclosure. The touch detection circuit 200 includes a detectioncapacitor 20, a charging circuit 21 c, a discharging circuit 21 d, acomparing circuit 23, a counter 25 and a processor 27, wherein theprocessor 27 is, for example, a digital signal processor (DSP) orapplication specific integrated circuit (ASIC) that performs thefunction thereof using hardware and/or firmware. In one aspect, thecharging circuit 21 c, the discharging circuit 21 d, the comparingcircuit 23, the counter 25 and the processor 27 together form adetection chip electrically connected to the detection capacitor 20.

The detection capacitor 20 is generally in a form of electrode, and hascapacitance Csef to form a capacitor voltage Vc cross terminals thereofwhen receiving electricity. The detection capacitor 20 is arranged on acomponent, such as, but not limited to, a door handle, an applianceswitch or a lamp switch, for detecting a conductor (e.g., a hand) Whenthe conductor approaches or touches the detection capacitor 20, thecapacitance Csef is changed and such capacitance change is used as thedetecting mechanism of a sensitive switch.

As shown in FIG. 2 , one end of the detection capacitor 20 is connectedto a ground voltage, and the other end thereof is connected to thecharging circuit 21 c, the discharging circuit 21 d and the comparingcircuit 23.

The capacitor voltage Vc changes (shown as ΔVc in FIG. 4 ) with thecharging and discharging process. When the capacitance Csef is changed,charging and discharging times are also changed and such time change isused as the mechanism of identifying a touch event.

The charging circuit 21 c includes a variable current source 21 c 1 anda switching element 21 c 3 cascaded together, wherein the switchingelement 21 c 3 is, for example, a transistor switch. In one non-limitingaspect, the variable current source 21 c 1 includes multiple currentsources 31 and multiple current switches 33 to form a current bank asshown in FIG. 3 , wherein the current switches 33 are, for example,transistor switches.

Please referring to FIG. 4 together, it is a schematic diagram ofcharging and discharging of a touch detection circuit 200 according toone embodiment of the present disclosure. The charging circuit 21 c isused to charge the detection capacitor 20 within a first charginginterval t1 using a first charging current Ic1, and charge the detectioncapacitor 20 within a second charging interval t2 using a secondcharging current Ic2 smaller than the first charging current Ic1. Forexample, the first charging interval t1 and the second charging intervalt2 form one complete charging interval. Within the complete charginginterval, the charging circuit 21 c charges the detection capacitor 20using the first charging current Ic1 at first, and then charges thedetection capacitor 20 using the second charging current Ic2.

In FIGS. 2 and 4 , the charging and discharging current is shown as Icd.When the detection capacitor 20 is being charged, Icd is shown to havepositive values; whereas, when detection capacitor 20 is beingdischarged, Icd is shown to have negative values, or vice versa. Thepositive and negative values herein are only intended to illustrate acurrent flow direction, but not to limit the present disclosure.

Charging/discharging the detection capacitor 20 using a large currentcan shorten the charging interval but can have lower sensitive and noiseimmunity; whereas, charging/discharging the detection capacitor 20 usinga small current can have higher sensitivity, but a longer charginginterval is required to extend the scanning time. The present disclosuretakes features of both, and considers the first charging interval t1 asa charging reference time that has a substantially constant value evenwhen the capacitance Csef is changed by an external conductor. Theprocessor 27 controls the variable current source 21 c 1 (i.e.controlling the first charging current Ic1 and the second chargingcurrent Ic2) and the switching element 21 c 3 of the charging circuit 21c to cause the second charging interval t2 to be longer than the firstcharging interval t1. That is, the processor 27 controls the chargingreference time (i.e. t1) to be shorter than a half of the charginginterval. Preferable, under the circuit limitation, the first charginginterval t1 is set as short as possible, and the second charginginterval t2 is set as long as possible.

In the aspect shown in FIG. 3 , the processor 27 alters the firstcharging current Ic1 and the second charging current Ic2 by changingconducting or connecting states between the multiple current switches 33and the multiple current sources 31, e.g., more current switches 33being conducted, higher charging current being generated.

The discharging circuit 21 d includes a variable current source 21 d 1and a switching element 21 d 3 cascaded together, wherein the switchingelement 21 d 3 is, for example, a transistor switch. Similarly, in onenon-limiting aspect the variable current source 21 d 1 includes multiplecurrent sources 31 and multiple current switches 33 as shown in FIG. 3 .

Please referring to FIG. 4 again, the discharging circuit 21 d is usedto discharge the detection capacitor 20 within a first discharginginterval t3 using a first discharging current Id1, and discharge thedetection capacitor 20 within a second discharging interval t4 using asecond discharging current Id2 smaller than the first dischargingcurrent Id1. For example, the first discharging interval t3 and thesecond discharging interval t4 form one complete discharging interval.Within the complete discharging interval, the discharging circuit 21 ddischarges the detection capacitor 20 using the first dischargingcurrent Id1 at first, and then discharges the detection capacitor 20using the second discharging current Id2.

In the present disclosure, the first discharging interval t3 isconsidered as a discharging reference time that has a substantiallyconstant value even when the capacitance Csef is changed by an externalconductor. The processor 27 controls the variable current source 21 d 1(i.e. controlling the first discharging current Id1 and the seconddischarging current Id2) and the switching element 21 d 3 of thedischarging circuit 21 d to cause the second discharging interval t4 tobe longer than the first discharging interval t3. That is, the processor27 controls the discharging reference time (i.e. t3) to be shorter thana half of the discharging interval. Preferable, under the circuitlimitation, the first discharging interval t3 is set as short aspossible, and the second discharging interval t4 is set as long aspossible.

In the aspect shown in FIG. 3 , the processor 27 alters the firstdischarging current Id1 and the second discharging current Id2 bychanging conducting or connecting states between the multiple currentswitches 33 and the multiple current sources 31, e.g., more currentswitches 33 being conducted, higher discharging current being generated.

The comparing circuit 23 compares the capacitor voltage Vc with a firstreference voltage V_(H) and a second reference voltage V_(L) (e.g.,smaller than the first reference voltage V_(H)) to conduct/connect thecharging circuit 21 c to the detection capacitor 20 or conduct/connectthe discharging circuit 21 d to the detection capacitor 20. For example,when the charging circuit 21 c charges the detection capacitor 20 tocause the capacitor voltage Vc to reach the first reference voltageV_(H), the output signal of the comparing circuit 23 dis-conducts theswitching element 21 c 3 and conducts the switching element 21 d 3 tocause the discharging circuit 21 d to discharge the detection capacitor20; whereas, when the capacitor voltage Vc is discharged to reach thesecond reference voltage V_(L), the output signal of the comparingcircuit 23 dis-conducts the switching element 21 d 3 and conducts theswitching element 21 c 3 to cause the charging circuit 21 c to chargethe detection capacitor 20; and the detection capacitor 20 is chargedand discharged repeatedly in this way.

In one non-limiting aspect, the comparing circuit 23 includes twocomparators respectively taking the first reference voltage V_(H) andthe second reference voltage V_(L) as an input signal of one of twoinput terminals, and the other input terminal of the two comparators iscoupled to the capacitor voltage Vc. The output of one of the twocomparators is used to control ON/OFF of the switching element 21 c 3,and the output of the other one of the two comparators is used tocontrol ON/OFF of the switching element 21 d 3.

In another non-limiting aspect, the comparing circuit 23 includes onecomparator and one multiplexer. One input terminal of the comparatorreceives the first reference voltage V_(H) or the second referencevoltage V_(L) via the multiplexer, and the other input terminal of thecomparator is coupled to the capacitor voltage Vc. The output of thecomparator is used to control ON/OFF of the switching elements 21 c 3and 21 d 3.

It should be mentioned that a structure of the comparing circuit 23 isnot limited to those mentioned herein as long as it is able to comparethe capacitor voltage Vc with the first reference voltage V_(H) and thesecond reference voltage V_(L) to accordingly control charging ordischarging by controlling ON/OFF of the switching elements 21 c 3 and21 d 3.

In FIG. 2 , an inverter in the discharging circuit 21 d is used toindicate the switching elements 21 c 3 and 21 d 3 are not turned on/offtogether, but not to limit the present disclosure. For example, theinverter may be arranged in the charging circuit 21 c, or the comparingcircuit 23 sends out opposite signals to respectively control theswitching elements 21 c 3 and 21 d 3 without using an inverter in thecharging or discharging circuit.

The counter 25 (or called timer) sequentially counts/times lengths ofthe first charging interval t1, the second charging interval t2, thefirst discharging interval t3 and the second discharging interval t4,and a summation of t1 to t4 is used as a detection cycle.

In one aspect, the processor 27 identifies a touch event according tothe second charging interval t2 and the second discharging interval t4,without according to the first charging interval t1 and the firstdischarging interval t3. As mentioned above, the charging reference time(i.e. t1) and the discharging reference time (i.e. t3) do not changewith approaching of a conductor, and thus they are considered asbaseline time that reflects the baseline voltage of the detectioncapacitor 20. Accordingly, although the counter 25 is counting the wholedetection cycle (t1+t2+t3+t4), the processor 27 subtracts the chargingreference time t1 and the discharging reference time t3 from thedetection cycle (t1+t2+t3+t4) to generate a time of interest (TOI), i.e.a summation of the second charging interval and the second discharginginterval (t2+t4).

The processor 27 identifies whether a touch event occurs according to avariation of TOI (t2+t4) between successive detection cycles. Forexample, when the variation of TIO (t2+t4) is larger than a variationthreshold, the processor 27 confirms the occurrence of a touch event andthen sends a control signal Sc to open a door or turn on/off anappliance or lamp according to different applications; on the contrary,it means no conductor being approaching.

For example, FIG. 4 shows that when a touch event occurs, the variationof capacitor voltage ΔVc is changed from the solid line to the dashedline to cause the TOI (t2+t4) to be extended to (t2′+t4′). Accordingly,when a value of (t2′+t4′)−(t2+t4) exceeds the variation threshold, theprocessor 27 confirms the occurrence of a touch event.

In addition, the processor 27 may identify whether a touch event occursaccording to a comparison result of comparing the variation of detectioncycle (t1+t2+t3+t4) and a predetermined threshold, i.e. calculating(t1+t2′+t3+t4′)−(t1+t2+t3+t4).

In addition, when the variation of a single TOI or a single detectioncycle caused by the change of capacitance Csef is too small, theprocessor 27 further identifies whether a touch event occurs accordingto the variation of multiple TOI, i.e. N×(t2+t4) or multiple detectioncycles N×(t1+t2+t3+t4).

In one aspect, when identifying that the detection cycle (t1+t2+t3+t4)is equal to or close to a noise cycle (or detection frequency equal toor close to noise frequency), the processor 27 further changes the firstcharging current Ic1 and the first discharging current Id1 (or alsochanging the second charging current Ic2 and the second dischargingcurrent Id2) to alter the detection cycle such that the noise frequencyband is avoided to improve the detection accuracy. For example, theprocessor 27 is further embedded with a time domain-frequency domainconversion algorithm for calculating the noise frequency. The method ofcalculating the noise frequency or cycle is known to the art, and thusnot described herein.

Referring to FIG. 5 , it is a flow chart of an operating method of atouch detection circuit 200 according to one embodiment of the presentdisclosure, including the steps of: charging, using a charging circuit21 c, a detection capacitor 20 using a first charging current Ic1, andcounting a first charging interval t1 using a counter 25 (Step S51);charging, using the charging circuit 21 c, the detection capacitor 20using a second charging current Ic2, smaller than the first chargingcurrent Ic1, and counting a second charging interval t2 using thecounter 25 (Step S52); discharging, using a discharging circuit 21 d,the detection capacitor 20 using a first discharging current Id1, andcounting a first discharging interval t3 using the counter 25 (StepS53); discharging, using the discharging circuit 21 d, the detectioncapacitor 20 using a second discharging current Id2, smaller than thefirst discharging current Id1, and counting a second discharginginterval t4 using the counter 25 (Step S54); and identifying a touchevent according to a time variation of multiple summations of the secondcharging interval t2 and the second discharging interval t4. The timevariation of multiple summations of the second charging interval t2 andthe second discharging interval t4 is N×(t2′+t4′)−N×(t2+t4).

As mentioned above, using multiple charging and discharging intervals isto avoid the scenario that the variation of a single charging anddischarging interval is smaller than detection sensitivity. In thepresent disclosure, N is larger than or equal to 1.

Details of this operating method have been illustrated above, and thusare not repeated herein.

As mentioned above, the processor 27 may identify a touch eventaccording to the variation of a summation (t2+t4) of the second charginginterval t2 and the second discharging interval t4 between successivedetection cycles, and the first charging interval t1 and the firstdischarging interval t3 are used as the baseline time but not foridentifying the touch event.

The operating method of this embodiment further includes the step of:comparing, using a comparing circuit 23, a capacitor voltage Vc of thedetection capacitor 20 with a first reference voltage V_(H) and a secondreference voltage V_(L) to determine whether to charge or discharge thedetection capacitor 20.

In some aspects, the comparing circuit 23 further includes a flip-flopto provide a “1” or “0” level for being counted by the counter 25according to the output of the comparator included in the comparingcircuit 23.

It should be mentioned that the value in the above embodiment, e.g., alength of charging and discharging shown in FIG. 4 , is only intended toillustrate but not to limit the present disclosure.

It should be mentioned that although the above embodiments areillustrated in a way that two different currents are used to charge thedetection capacitor 20 within a charging interval and two differentcurrents are used to discharge the detection capacitor 20 within adischarging interval, the present disclosure is not limited thereto. Inother aspects, more than two different currents are used to charge thedetection capacitor 20 within the charging interval and more than twodifferent currents are used to discharge the detection capacitor 20within the discharging interval. The processor 27 identifies a touchevent according to charging and discharging intervals corresponding tothe minimum charging current and the minimum discharging current.

It should be mentioned that although the above embodiments areillustrated in a way that the touch detection circuit 200 includes asingle self-capacitive electrode (e.g., forming the detection capacitor20), the present disclosure is not limited thereto. In other aspects,the touch detection circuit 200 includes multiple parallelself-capacitive electrodes each being connected to the respectivecharging circuit, discharging circuit, comparing circuit and counter asshown in FIG. 2 . The operation of each self-capacitive electrode isidentical to the descriptions mentioned above. The counting results ofmultiple counters are sent to the same processor 27. When identifyingthat the counted time variation associated with at least oneself-capacitive electrode or with a predetermined number ofself-capacitive electrodes exceeds a variation threshold, the occurrenceof a touch event is confirmed.

It should be mentioned that although the present disclosure isillustrated using the touch detection circuit, the touch detectioncircuit is not only used to detect a touch. When a conductor approachesthe detection capacitor 20 (to influence the detection capacitor), eventhough the conductor is not actually in contact with the detectioncapacitor 20 (or the component arranged with the detection capacitor20), the touch detection circuit still detects an approaching conductoras long as the variation of charging and discharging interval (i.e.indicating variation of capacitance) exceeds a threshold, wherein adetectable distance is determined according to the threshold being set.That is, a touch event detected by the touch detection circuit 200 ofthe present disclosure includes the object touch and the objectproximity.

As mentioned above, the conventional capacitive switch is easilyaffected by environmental change and noises to degrade the detectionaccuracy. Accordingly, the present disclosure further provides a touchdetection circuit (e.g., FIG. 2 ) and an operating method thereof (e.g.,FIG. 5 ) that charge and discharge a detection capacitor using a largecurrent and a small current. The charging and discharging intervalassociated with the larger current is considered as baseline time andcancelled in identifying the touch event. Furthermore, when a frequencyof charging and discharging the detection capacitor is close to thenoise frequency, the frequency of charging and discharging is changed bychanging the charging and discharging currents to avoid the noisefrequency band.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A touch detection circuit, comprising: adetection chip, configured to be coupled to an electrode, and charge theelectrode within a first charging interval using a first chargingcurrent, and charge the electrode using a second charging current,smaller than the first charging current, till a first reference voltageis reached, discharge the electrode within a first discharging intervalusing a first discharging current, and discharge the electrode using asecond discharging current, smaller than the first discharging current,till a second reference voltage, which is smaller than the firstreference voltage, is reached, and identify approaching of the externalconductor according to a second charging interval during which theelectrode is charged by the second charging current and a seconddischarging interval during which the electrode is discharged by thesecond discharging current without according to the first charginginterval and the first discharging interval.
 2. The touch detectioncircuit as claimed in claim 1, wherein the detection chip comprises: acharging circuit, configured to provide the first charging current andthe second charging current; a discharging circuit, configured toprovide the first discharging current and the second dischargingcurrent; and a comparing circuit, configured to compare a voltage on theelectrode with the first reference voltage and the second referencevoltage for conducting the charging circuit to the electrode orconducting the discharging circuit to the electrode.
 3. The touchdetection circuit as claimed in claim 2, wherein the charging circuitand the discharging circuit respectively comprise a variable currentsource and a switching element, and the detection chip is furtherconfigured to control the variable current source and the switchingelement of the charging circuit to cause the second charging interval tobe larger than the first charging interval, and control the variablecurrent source and the switching element of the discharging circuit tocause the second discharging interval to be larger than the firstdischarging interval.
 4. The touch detection circuit as claimed in claim3, wherein the first charging interval, the second charging interval,the first discharging interval and the second discharging interval areconfigured as a detection cycle, the first charging interval is prior tothe second charging interval within the detection cycle, and the firstdischarging interval is prior to the second discharging interval withinthe detection cycle.
 5. The touch detection circuit as claimed in claim4, wherein the detection chip is further configured to change the firstcharging current and the first discharging current to alter thedetection cycle when the detection cycle is equal to a noise cycle. 6.The touch detection circuit as claimed in claim 5, wherein the chargingcircuit and the discharging circuit respectively comprise multiplecurrent sources and multiple current switches, and the detection chip isconfigured to change the first charging current and the firstdischarging current by changing conducting states between the multiplecurrent sources and multiple current switches.
 7. The touch detectioncircuit as claimed in claim 1, wherein when a variation of a summationof the second charging interval and the second discharging interval islarger than a variation threshold, the detection chip identifiesoccurrence of a touch event.
 8. The touch detection circuit as claimedin claim 1, wherein the first charging interval and the firstdischarging interval are respectively a constant value.
 9. The touchdetection circuit as claimed in claim 1, wherein the first charginginterval and the second charging interval form a complete charginginterval, and the first charging interval is smaller than a half of thecomplete charging interval, and the first discharging interval and thesecond discharging interval form a complete discharging interval, andthe first discharging interval is smaller than a half of the completedischarging interval.
 10. The touch detection circuit as claimed inclaim 1, wherein the detection chip comprises a timer configured to timelengths of the first charging interval, the second charging interval,the first discharging interval and the second discharging interval. 11.A capacitive switch, comprising: an electrode, having capacitance; and adetection chip, coupled to the electrode, and configured to charge theelectrode sequentially using a first charging current and a secondcharging current, smaller than the first charging current, within acharging interval, discharge the electrode sequentially using a firstdischarging current and a second discharging current, smaller than thefirst discharging current, within a discharging interval, exclude timeintervals associated with the first charging current and the firstdischarging current from a summation of the charging interval and thedischarging interval to determine a time of interest, and output acontrol signal by comparing the time of interest with a variationthreshold.
 12. The capacitive switch as claimed in claim 11, wherein thedetection chip is configured to charge the electrode within a chargingreference time, which is a constant value, using the first chargingcurrent, and discharge the electrode within a discharging referencetime, which is a constant value, using the first discharging current.13. The capacitive switch as claimed in claim 12, wherein the detectionchip comprises: a charging circuit, configured to provide the firstcharging current and the second charging current; a discharging circuit,configured to provide the first discharging current and the seconddischarging current; and a comparing circuit, configured to compare avoltage on the electrode with a first reference voltage and a secondreference voltage for conducting the charging circuit to the electrodeor conducting the discharging circuit to the electrode.
 14. Thecapacitive switch as claimed in claim 13, wherein the charging circuitand the discharging circuit respectively comprise a switching element,and the detection chip is further configured to control the switchingelement of the charging circuit to cause the charging reference time tobe smaller than a half of the charging interval, and control theswitching element of the discharging circuit to cause the dischargingreference time to be smaller than a half of the discharging interval.15. The capacitive switch as claimed in claim 13, wherein the charginginterval and the discharging interval form a detection cycle, and thedetection chip is further configured to change the first chargingcurrent and the first discharging current to alter the detection cyclewhen the detection cycle is equal to a noise cycle.
 16. The capacitiveswitch as claimed in claim 15, wherein the charging circuit and thedischarging circuit respectively comprise multiple current sources andmultiple current switches, and the detection chip is configured tochange the first charging current and the first discharging current bychanging conducting states between the multiple current sources andmultiple current switches.
 17. The capacitive switch as claimed in claim11, wherein the detection chip comprises a timer configured to timelengths of the charging interval and the discharging interval.
 18. Anoperating method of a touch detection circuit, the touch detectioncircuit comprising an electrode and a detection chip, the operatingmethod comprising: charging, using the detection chip, the electrodeusing a first charging current within a first charging interval;charging, using the detection chip, the electrode using a secondcharging current, smaller than the first charging current within asecond charging interval; discharging, using the detection chip, theelectrode using a first discharging current within a first discharginginterval; discharging, using the detection chip, the electrode using asecond discharging current, smaller than the first discharging current,within a second discharging interval; and identifying a touch eventaccording to a time variation of multiple summations of the secondcharging interval and the second discharging interval.
 19. The operatingmethod as claimed in claim 18, wherein the touch event is not identifiedusing the first charging interval and the first discharging interval.20. The operating method as claimed in claim 18, further comprising:comparing, using the detection chip, a voltage on the electrode with afirst reference voltage and a second reference voltage to determinewhether to charge or discharge the electrode.